An organic EL device is a spontaneous light emitting device which utilizes such a principle that a fluorescent substance emits light by virtue of recombination energy of holes injected from an anode and electrons injected from a cathode by an application of an electric field. Since an organic EL device of the laminate type capable of being driven under low electric voltage has been reported by C. W. Tang et al. of Eastman Kodak Company (C. W. Tang and S. A. Vanslyke, Applied Physics Letters, Volume 51, Page 913, 1987, or the like), many studies have been conducted for an organic EL device using an organic material as a constituent material. Tang et al. used tris(8-quinolinolato)aluminum for a light emitting layer and a triphenyldiamine derivative for a hole transporting layer. Advantages of the laminate structure reside in the followings: an efficiency of the hole injection into the light emitting layer can be increased; an efficiency of forming exciton which are formed by blocking and recombining electrons injected from the cathode can be increased; and exciton formed within the light emitting layer can be enclosed. As described above, for the structure of the organic EL device, a two-layered structure having a hole transporting (injecting) layer and an electron transporting light emitting layer and a three-layered structure having a hole transporting (injecting) layer, a light emitting layer, an electron transporting (injecting) layer, and the like are widely known. In order to increase the efficiency of recombination of injected holes and electrons in the devices of the laminate type, the device structure and the process for forming the device have been studied.
In general, when an organic EL device is driven or stored in an environment of high temperature, there occur adverse effects such as a change in the luminescent color, a decrease in current efficiency, an increase in driving voltage, and a decrease in a lifetime of light emission. In order to prevent the adverse effects, it has been necessary that the glass transition temperature (Tg) of the hole transporting material be elevated. Therefore, it is necessary that many aromatic groups be held within a molecule of the hole transporting material (for example, an aromatic diamine derivative of Patent Document 1 and a fused aromatic ring diamine derivative of Patent Document 2), and in general, a structure having 8 to 12 benzene rings are preferably used.
However, when a large number of aromatic groups are present in a molecule, crystallization is liable to occur upon production of the organic EL device through the formation of a thin film by using those hole transporting materials. As a result, there arises a problem such as clogging of an outlet of a crucible to be used in vapor deposition or a reduction in yields of the organic EL device due to generation of defects of the thin film resulting from the crystallization. In addition, a compound having a large number of aromatic groups in any one of its molecules generally has a high glass transition temperature (Tg), but has a high sublimation temperature. Accordingly, there arises a problem in that the lifetime of the compound is short, because a phenomenon such as decomposition at the time of the vapor deposition or the formation of a nonuniform deposition is expected to occur.
On the other hand, there is a known document disclosing an asymmetric aromatic amine derivative. For example, in Patent Document 3, there is described an aromatic amine derivative having an asymmetric structure, but there is no specific example thereof, and also, there is no description of a feature of the asymmetric compound at all. Further, in Patent Document 4, an asymmetric aromatic amine derivative containing phenanthrene is described as an example, but the derivative is lumped into the same category as symmetric compounds and there is no description of a feature of the asymmetric compound at all. Further, although the asymmetric compound needs a special synthesis method, a description on a production method of the asymmetric compound is not clearly disclosed in those patent documents. Also, in Patent Document 5, there is a description on the production method of the aromatic amine derivative having an asymmetric structure, but there is no description of a feature of the asymmetric compound. In Patent Document 6, there is a description on an asymmetric compound which has a high glass transition temperature and is thermally stable, but only a compound containing carbazole is exemplified.
Further, Patent Documents 7 and 8 are reports on amine compounds each having thiophene. Those are compounds which each have thiophene in a central skeleton of a diamine compound. Further, in the compound of Patent Document 7, the thiophene is directly bonded to amine. Patent Documents 9 and 10 are given as reports on a compound having thiophene at a terminal of a diamine compound, and in those compounds, thiophene is directly bonded to amine. Those compounds are unstable and the purification thereof is difficult; therefore, the purity thereof does not improve. Further, when the thiophene is directly bonded to the amine, an electronic state of the amine largely changes; therefore, sufficient performance cannot be obtained in the case where each of the compounds is used as a material for the organic EL device. On the other hand, in Patent Document 11, there is a description on compounds in which the thiophene is bonded to the amine through an aryl group. However, those compounds have a structure including an unsubstituted thiophene at 2- or 5-position thereof. 2- or 5-position of thiophene has high reactivity and is electrically unstable, and when the thiophenes are present in the molecule, a high voltage is required in the case where the compounds are each used as a device; therefore, those compounds are not preferred. Patent Document 12 is given as the description of amine polymers, but there is only specific examples and is no description on the amine compound in which the thiophene is bonded to nitrogen through the aryl group at all. A polymer is described in Patent Documents 13 to 22, but cannot be subjected to vapor deposition. Further, a polar group required for polymerization decreases the lifetime as a device; thus, the polar group is not preferred.
As described above, it is generally known that the compound having a thiophene structure has a high mobility, but a sufficient performance cannot be obtained, when used as a material of the organic EL device, by merely combining the compound with an amine structure. Therefore, development of a material for an organic EL device having further improved performance has been strongly desired.    [Patent Document 1] U.S. Pat. No. 4,720,432    [Patent Document 2] U.S. Pat. No. 5,061,569    [Patent Document 3] JP 08-48656 A    [Patent Document 4] JP 11-135261 A    [Patent Document 5] JP 2003-171366 A    [Patent Document 6] U.S. Pat. No. 6,242,115    [Patent Document 7] WO 2004-058740    [Patent Document 8] JP 04-304466 A    [Patent Document 9] WO 2001-053286    [Patent Document 10] JP 07-287408 A    [Patent Document 11] JP 2003-267972 A    [Patent Document 12] JP 2004-155705 A    [Patent Document 13] JP 2005-042004 A    [Patent Document 14] JP 2005-259441 A    [Patent Document 15] JP 2005-259442 A    [Patent Document 16] JP 2005-235645 A    [Patent Document 17] JP 2005-235646 A    [Patent Document 18] JP 2005-082655 A    [Patent Document 19] JP 2004-288531 A    [Patent Document 20] JP 2004-199935 A    [Patent Document 21] JP 2004-111134 A    [Patent Document 22] JP 2002-313574 A